In general, leuco color-forming type heat-sensitive recording materials are used as those for heat-sensitive recording methods. However, the heat-sensitive recording materials have a drawback in that an unexpected part is often colored by severe handling after recording or by heat or adhesion of solvents, so that the images recorded would be stained. Recently, diazo series heat-sensitive recording materials have been studied as heat-sensitive recording materials which are free from the above noted drawback. For example, as illustrated in Japanese Patent Application (OPI) No. 123086/82 (the term "OPI" as used herein means a "published unexamined Japanese patent application"), Journal of Image Electronics Association of Japan, 11, 290 (1982), a recording material comprising a diazo compound, a coupling component and a basic component (including a substance capable of becoming basic under heat) is recorded under heat and then exposed to light so as to decompose the non-reacted diazo compound to stop the coloration. It is possible, in accordance with the recording method, to stop the coloration of the part which is unnecessary to be recorded (hereinafter referred to as "fixation"). However, pre-coupling gradually proceeds also in the recording material during storage so that the material is defectively and unfavorably colored (fogged).
In order to overcome this defect, Japanese Patent Application (OPI) No. 190886/84, discloses providing a heat-sensitive recording material comprising microcapsules, which contain at least one component participating in a color-forming reaction as a core substance, coated with a wall formed by polymerization therearound.
However, even the heat-sensitive recording material formed by this method is often stained because of pre-coupling during storage. In addition, a more rapid heat-responsibility is required for the recording material. Accordingly, improvement of known heat-sensitive recording materials is desired in this technical field.